Personally, I now prefer "Geany" simply because it is fast and lightweight and "just works" I used to love Eclipse but release after release it just felt heavier, slower and slower in the end I ditched it and went Geany. Honestly best decision I ever made!

Geany is awesome. I've been using it for a few years now. Rather simple and no-frills, but with some plugins it works pretty much exactly how I expect a code editor to work and has all the features I need. A hearty recommendation from me as well.

I use geany for all my development needs at work ( PHP ) - but it's only an editor not an idea.
I tried and really liked Brackets.io, sadly it's it doesn't support live edit via FTP which makes it rather useless for the way I develop. ( Fireftp on the dev server -> open in geany, save auto pushes the file )

For C++ development I've stuck to Code::Blocks, mostly I suspect because it reminds me of Dev-C++

I've tried both Anjuta and Eclipse, but they both seem to think that they should taker over the organization of my files which I really dislike.

Mousepad: Not an IDE, but I use it for my bash scripts . It has syntax colouring.

Geany: For my bigger projects in C or Go. It has limited features but it works well enough and is lightweight. It has syntax colouring AND completion based on the functions and variables in the current file at least. I wish I could switch between projects (open tabs/files); maybe it’s possible already?

Qt-Creator: For a big C++ open-source project that uses Qt so it was a no-brainer. It has useful features like "Find usage" to know where a function is used (doesn’t work well for virtual functions unfortunately, at least in Qt Creator 2.8; perhaps I need to upgrade?) Not perfect but a good IDE.

Ten years ago I used Code::Blocks for my own project and it worked well.

Emacs. I think it qualifies as an IDE but it's not just that. Getting to do email, bookmarking & notes, chat and so on in the same app and being able to modify absolutely everything and being able to write a bit of elisp every time you get an idea for something that would make your workflow smoother is amazing. I do recommend not sticking with the default keybindings for the most often used stuff though, taking inspiration from something like Ergoemacs is better.

I like QtCreator for C/C++ (earlier I used Code::Blocks, but that was too unstable for me, so I looked for something different), but I'm thinking about switching to KDevelop 5. For Python I have to use PyCharm because my university wants me to. When I did much with Java, I used Eclipse. For everything else I prefer a simple Kate (or gedit when I'm not on a KDE Desktop).